Low explosive primerless formed charges



March 12, 1968 R. c. KVAVLE 3,372,643

LOW EXPLOSIVE PRI MERLESS FORMED CHARGES Filed Fb. 1, 1966 Inven tar R0 berz C Kuavle B5 hzls Attorney United States atent 3,372,643 LOW EXELOSIVE PRIMERLESS FORMED CHARGES Robert C. Kvavle, Hillsboro, Oreg, assignor to United Shoe Machinery Corporation, Boston, Mass, 2 corporation of New Jersey Filed Feb. 1, 1966, Ser. No. 524,168 16 Claims. (Cl. 102-99) ABSTRACT OF THE DISCLOSURE A primerless, low explosive nitrocellulose charge is adapted by its apparent density and preferably also by configuration, to be easily ignited in a substantially closed chamber by friction due to direct impact and without reliance upon diesel type ignition.

This invention relates to low explosive, formed charges, and more particularly to a pellet or capsule for providing operating energy to a device upon its impact ignition and deflagration therein. The invention is herein illustrated as embodied in two configurations which are preferred for use in manually controlled, explosively actuated tools, but it will be appreciated that the charge is not necessarily thus limited in shape, it being recognized that various modifications may be desirable, within selected ranges of physical characteristics, to alter the potential energy of a given charge or its rate of deflagration, or to suit a particular ignition cavity.

As disclosed in an application for US. Letters Patent Ser. No. 371,242, now Patent 3,283,657, relating to an impact ignition type tool and a method of ignition therefor and filed May 29, 1964, in my name, there is considerable need for a safe, low cost, primerless, and relatively stable explosive as the energy source for various devices, for instance portable tools for driving fasteners. Hitherto a sensitive primer has been commonly used to initiate ignition, or the charge has been ignited by electrical energy, or a rise in temperature effected by the compression of air or air with specially added gases or vapors. Such alternate approaches generally fail to provide reliable, simple means for ignition, or afford expensive energy compared to that resulting from the use of a system employing impact ignition of low explosive in a substantially closed chamber. While there are a number of known and available low explosives including, for example, the better known gunpowder and nitrated cellulose wherein the nitrogen content does not exceed about 13 /2 by weight, it is important that the low explosive, especially for industrial use, be available in a convenient, easily handled form, that it be at least relatively noncorrosive, perform uniformly over a wide range of prevailing temperatures with predictable energy release, and that it have fairly long shelf life without appreciable physical or chemical change.

In the light of the foregoing it is a primary object of this invention to provide a charge of low explosive which is adapted to be safely yet easily deflagrated by a controlled, non-diesel impact and which shall have the favorable attributes above mentioned.

Another object of the invention is to provide this preferred charge in an advantageous form facilitating its feeding, ignition and storage.

A further object of the invention is to provide a low explosive capsule requiring minimal energy little or none of which need be expended in compressing ambient gas, to obtain its ignition, and which charge is entirely consumable, that is, will leave substantially no residue other than the gases evolved in deflagration.

To these ends, and in accordance with a feature of the present invention, fibrous nitrated cellulose having a nitrogen content on the order to 13 /2% by weight is compacted and molded to an advantageous pellet shape from its ordinary commercially available powdered state, the pellet retaining a porosity such that its gross or apparent density comes Within the range of 0.6 gram per cc. to 1.55 grams per cc. and preferably having a thinner internal portion adapted to be crushed by impact to facilitate ignition and hence defiagration of the entire molded charge.

A further feature of the invention resides in providing a pellet molded of nitrocellulose as just described wherein the thinner portion mentioned is a central recessed web having the shape and size substantially corresponding to the impacting surface of a firing pin whereby the latter is enabled to initiate ignition by occluding within the pellet a predetermined limited amount of air entrapped externally of the web and internally thereof.

Another feature of the invention as herein shown consists in the provision, of a cup-shaped nitrocellulose pellet of the type aforesaid, its base constituting the web thinner than its surrounding cylindrical wall and having a slightly thicker, preferably raised, central portion adapted to receive energy from a firing pin in a localized initial ignition area.

The foregoing and other features of the invention, including such novel details as locating the web substantially midway within a molded and otherwise hollow nitrocellulose charge having duplicate ends in order to facilitate handling or feeding, will now be more particularly described in connection with embodiments selected for purposes of illustration only, and with reference to the accompanying drawings thereof, in which:

FIG. 1 is a perspective view of an exemplary molded pellet consisting of a low explosive;

FIG. 2 is a diametric section of the charge shown in FIG. 1 and indicating (though not in true proportion) a thickened igniter portion; and

FIG. 3 is a diametric section of a modified form of my explosive capsule.

Referring first to FIGS. 1 and 2, there is shown one configuration of a capsule or pellet 10 to low explosive having special merit when employed to supply energy to a device, for instance a fastener driving tool. By low explosive is meant that class of explosive materials which will, upon ignition, progressively burn or deflagrate, and the definition is intended to exclude those more highly sensitive explosive materials which have their ignition characterized as detonation, a phenomenon which occurs much more violently and at about the speed of sound or roughly one-thousand times faster than usual defiagration. In the form of the explosive charge shown in FIGS. 1 and 2, the pellet 10 has a generally cylindrical or cupshaped body 12 and a thinner base or web 14. The entire pellet, exclusive of any or 'various diluents and additives, is preferably molded from a nitrocellulose fibre powder having a nitrogen content in the range of from l2 /2% to 15% by Weight. It is essential of course to take preventive precaution against premature explosion of any dust from such powder, but the fibrous nitrocellulose powder while in the normal atmosphere of a room and in reasonably dry condition may be safely compacted to mold it into conveniently useful configuration.

As taught in the above cited copending application Ser. No. 371,242, now Patent 3,283,657, ignition of a low explosive charge may be effected by direct mechanical impact therewith thus avoiding any need for using a primer or other complex ignition mechanism, and rendering an explosively actuated device, such as a fastener tool, more compact, safe, and portable. Of particular significance, as there described, is the fact that the relatively obdurate low explosive to be ignited by impact must be substantially confined so that only a limited amount of trapped air, preferably some surrounding and some entrapped within the charge itself, is available for aiding ignition and insuring that gas then evolved builds up pressure conductive to defiagrating the entire explosive charge. Unlike diesel type ignition, only this limited amount of air is desirable or needed, and no waste effort need be expended in compressing ambient air. Accordingly the pellet is desirably molded in a configuration to constitute an obturating liner for an ignition cavity wherein the explosive is to be used, the pellet 10 shown in FIGS. 1, 2 presuming a generally cylindrical ignition cavity of substantially corresponding size. A male forming die (not shown) is selected to correspond substantially in shape and size at its central portion with a firing pin (or a protrusion on such a pin) expected to be used, and would compact the charge material thus providing a central bore or recess 16 in the pellet which is ultimately used to entrap a predetermined volume of air aiding in ignition and/ or ensuing defiagraton.

In order to enable the formed charge to be ignited with only moderate impact energy, the thin base 14 preferably has a thickened central igniter portion 18 which, in this case, is raised to approximately double the base thickness surrounding the portion 18. This configuration is effected by a suitable corresponding recess in the chargeengaging end of the male mold. The reduced central portion 18 is shown as a truncated cone having a tapered wall 20 (FIG. 2) extending at about a 45 angle between the base 14 and the raised igniter or reduced central area adapted to be struck by a firing pin.

By way of example only, one pellet configuration according to the invention and adapted for use in a stud driving tool has an outside diameter of approximately an inside diameter of approximately 0.187", an overall thickness of about /3, a minimum base thickness of about 0.030 to 0.040" and a raised igniter portion of about 0.055 to 0.065. Since it is probable that the mechanics which facilitates impact ignition of low explosive is assisted by air entrapped between the molded nitrocellulose fibres themselves, i.e. in the continuous substantially interconnected interstitial spaces between the ribbon-like fibres, the molding process should compact the powder to the preferred self-sustaining form and still retain porosity, a suitable range of pellet density for nitrocellulose fibre having a nitrogen content on the order of 13.2% by Weight being on the order of about 0.6 gram to 1.55 grams per cubic centimeter, for example. Solid nitrocellulose, incidentally, i.e. nonporous, has a density of 1.6 grams per cc. Desirably, then, the raised igniter portion 18 may be more porous, its fibres defining substantially continuous burning surfaces, and be expected to entrap slightly more air than in the surrounding web, such entrapped air being advantageously available together with air compressed about the igniter portion in this critical locality for chemical decomposition when the firing pin kinetic energy is absorbed in frictionally crushing and initiating ignition in a space then enclosed by the pin end and the inside walls of the pellet. Experience indicates that as pellet density approaches the lower end of the density range noted above, the kinetic energy upon impact tends to produce localized incipient ignition that less reliably results in complete burning of the charge.

In stating that ignition of the pellet is initiated by friction incurred as a result of impact therewith, it is not intended to exclude the possibility that ignition may thus be initiated in the pellet at a resultant hot spot on or immediately adjacent to the impacted portion where a piezoelectric field is momentarily created.

Referring now to FIG. 3, a variant form of pellet of low explosive, preferably having substantially the same chemical composition as referred to above, is provided intermediate its height with a web 32 having a thickness which is less than that of the surrounding wall with which it is integral. The web 32 may have a centrally thickened igniter portion (not shown in FIG. 3) corresponding to that at 18 in FIGS. 1 and 2, but need not have such a portion. This is because it is a feature of the configuration now being described that its general symmetry and duplicate upper and lower face portions 34 avoid the problem of orienting each molded charge 30 to insure that one or the other face of the web 32 will confront a firing pin. The occlusion aflTorded by the pellet 30 is probably not as precise as that attained with the pellet 10; for most purposes, however, its precision is adequate though the molding dies Will not be quite as simple and slightly greater kinetic energy may be needed in the firing pin.

Operation of the molded pellets described is essentially the same. In impacting the Web 32 or the igniter portion 18 in a percussion cavity of a tool or device to be explosively actuated, the firing pin moving axially in a pellet crushes the nitrocellulose fibres after it has been received in the closely fitting pellet walls forming the recess 16. The impacting stroke of the pin may commence either when it is spaced axially or otherwise from the pellet, or it may start, as is often preferred, with the pin in an initial rest position of engagement with the pellet, for instance contacting a portion such as at 18 or 32 of the pellet. An advantage of such stationary pin contact with the pellet prior to ignition by frictional engagement therewith of the pin is that the pellet can thus be urged into self-sealing relation Within its firing chamber. The body of the pellet 10 or 30 is adapted to closely fit the percussion cavity so that gas pressure generated will not prematurely displace the pellet or blow it apart. It is believed that the impact action of the firing pin (or other equivalent striker means) closely fitting the recess 16 on the pellet is concomitant with an adiabatic pressure increase in the trapped and entrapped gas. It has been ascertained from trials that given a certain potential impact energy, the initial ignition is facilitated 'by the provision of the reduced igniter portion 18 for localizing pellet compression. Moreover, the molded composition and structure of the charge as described is found to be economical and reliable. Its corrosive effect on steel commonly used is minimal. If desired, the external walls of the pellet may be treated to shed water and moisture though such processing is probably unnecessary for many commercial uses, but probably desirable in the case of military use.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A primerless defiagrating charge for use in an explosively actuated device, said charge comprising a compacted body of nitrocellulose fibres having air in the substantially interconnected interstitial spaces between the fibres defining continuous burning surfaces, said charge having a density less than 1.6 grams per cc. yet more than about 0.6 gram per cc.

2. A primerless mechanically fired cartridge comprising a pellet of nitrated cellulose fibres, said pellet having air in the substantially interconnected interstitial spaces between the fibres defining continuous burning surfaces, and having suflicient resilience to act as an obturator in an enclosing chamber, the density of said pellet being less than that of nitrocellulose per se and sufficient to retain its self-sustaining form.

3. A low explosive pellet adapted to be entirely deflagrated in an impact ignition cavity, said pellet being annular in cross section and having a central recess adapted to serve as an igniter, the bottom of said recess being defined by a wall having a thickness less than that of the surrounding wall.

4. A relatively stable low explosive charge ignitable by impact to generate gas by defiagration, said charge comprising a pellet of nitrocellulose fibres molded into a self-sustaining porous form retaining entrapped air in its substantially interconnected interstitial spaces between the fibres, said pellet having an outer resilient Wall for lining an enclosing chamber wherein the charge is to be deflagrated, and an igniter portion recessed with respect to said outer wall, at least said igniter portion having a density less than nitrocellulose per se and its fibres defining continuous burning surfaces.

5. A wholly consumable caseless defiagrating charge to be ignited by impact therewith in a chamber, said charge comprising a substantially resilient pellet compacted from fibrous nitrocellulose and having a density less than nitrocellulose per se and having an igniter portion provided with a web thickness less than any other dimension of any other portion of the pellet.

6. A charge as set forth in claim wherein the nitrogen in the nitrocellulose fibre is within the range of 12.75% to 13.75% by weight.

7. A charge as set forth in claim 6 wherein the moisture content is less than 5% by Weight.

8. A charge as set forth in claim 6 wherein the pellet has a density in the range of from 0.9 gram per cubic centimeter to 1.55 grams per cubic centimeter.

9. A charge as set forth in claim 5 wherein the pellet is cylindrical and has an inner bore the bottom of which is determined by the igniter portion, the surface of said bore being smooth to cooperate in closely fitting relation with an impacting means.

10. A charge as set forth in claim 5 wherein the igniter portion constitutes a closure for a cylindrical recess in the pellet.

11. A charge as set forth in claim 5 wherein the igniter portion is thickened in one part thereof to facilitate initial ignition.

12. A charge as set forth in claim 10 wherein the igniter portion provides a flat external base for the pellet and has a central raised internal part adapted to be initially impacted.

13. A charge as set forth in claim 5 wherein the igniter portion is formed centrally as a truncated cone.

14. A defiagration pellet of low relatively stable explosive of hollow, cylindrical, configuration wherein there is disposed an integral transverse fibrous propellant web adapted to be ignited by localized friction due to impact directed axially of the pellet, at least said web comprising nitrocellulose fibres which have been compacted to entrap air for facilitating initiating deflagration of the pellet.

15. A pellet as set forth in claim 14 and further characterized in that said web is disposed intermediate duplicate axial end faces of the pellet.

16. For use in a gas generating chamber of an explosively actuated device, said chamber having a firing pin axially operable therein, a defiagration pellet comprising compacted fibrous nitrocellulose, the cross section of the pellet being such as to serve as an obturator and corresponding substantially to that of the chamber, and the pellet having an axial recess an end of which is defined in part by a raised igniter portion, the cross section of said recess corresponding substantially with that of at least a portion of said firing pin.

References Cited UNITED STATES PATENTS 552,919 l/1896 Maxim 102-101 3,283,657 11/1966 Kvavle 89'--7 X 3,302,319 2/1967 Rosselet 421 FOREIGN PATENTS 27,652 3/ 1964 Germany. 160,940 1884 Great Britain.

OTHER REFERENCES Military Pyrotechnics Series, AMC pamphlet AMCP 106187, part three, pp. 218-220, October 1963.

BENJAMIN A. BORCHELT, Primary Examiner. ROBERT F. STAHL, SAMUEL W. ENGLE, Examiners. 

